The present invention relates to an antilock braking system (ABS) of a heavy vehicle. It finds particular application in conjunction with a trailer ABS relay valve and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other applications.
It is not uncommon for heavy vehicles to include both a tractor and trailer. Tractor-trailer ABS units include a trailer ABS module including a valve that acts as a relay valve during normal braking, but during ABS events, helps improve stability. An air signal transmitted to a control port of the ABS module is transmitted to a control port of the relay valve via a solenoid valve, which is normally open during normal braking operation. For example, air transmitted to the ABS module control port may be transmitted to the relay valve control port (via the solenoid valve) for setting the relay valve in a delivery mode (e.g., passing compressed air from a supply port to a delivery port of the relay valve). During an ABS event, the solenoid is alternately switched between the normally open position and a closed position, which causes the brakes to be alternately applied.
At times, it is desirable to exhaust the compressed air at the relay valve control port. However, under certain conditions, when the solenoid valve is closed, compressed air from the ABS module control port becomes trapped at the relay valve control port.
Current ABS module designs include a one-way check valve for ensuring a pressure at the relay valve control port is not higher than a pressure at the ABS module control port. The check valve increases manufacturing costs and complexity of the ABS module.
The present invention provides a new and improved apparatus and method which addresses the above-referenced problems.